1. Field of the Invention
This invention generally relates to electronic sound generating devices. More particularly the invention relates to circuits for controlling and driving such devices and allowing the generation of a variety of sounds from such sound generating devices.
2. Description of the Related Art
Piezoelectric transducers have been commonly used for the generation of audio tones in a number of applications. They are characterized by low cost, reliability and high audio output. A drawback of the use of one type of piezoelectric transducer, piezoelectric benders, to generate the tones is the relatively high Q of such circuit elements, requiring a precise drive frequency for maximum output, and the high voltages needed to generate the high output sound levels.
Traditionally piezoelectric audible alarms have been driven by square wave drives from oscillator circuits. The high voltages desirable across the driven piezoelectric device are achieved by driving bridge drivers, step-up transformers or autotransformers or through an inductor in a flyback mode. This allows little flexibility once the components are inserted into the circuit. The use of a fixed digital drive in particular allows little adjustment of the sound volume. Coil speakers or polymer piezoelectric speakers have also been used as audio transducers and present similar problems in designing flexible drive circuits.
It is the object of the invention to provide a circuit and method of signal modulation for the audio transducer to provide both high drive power and flexible control.